1. Field of the Disclosure
The present disclosure generally relates a low profile internal tree cap and a system and method for installing a low profile internal tree cap in a subsea wellhead. The low profile internal tree cap may include various fluid passageways to permit the removal of trapped fluid during the installation of the tree cap. The internal tree cap may include means for sealing on the outer diameter of the upper neck of the tubing hanger. Alternatively, the internal tree cap may include means for sealing in the upper plug seal profile of a tubing hanger or tubing hanger crossover. The internal tree cap may include bi-directional metal-to-metal seals allowing the tree cap to be used on a gas lift well.
2. Description of the Related Art
A subsea wellhead assembly often includes a tree spool used to access the well bore. A tree cap may be used to seal off the tree spool while also permitting access to the tree spool. The tree cap typically includes one or more seals that are disposed between the tree cap and the tree spool to provide a seal between the tree cap and the tree spool. While installing a tree cap in a subsea tree one potential problem is damaging the seals during the installation process. The seals are the key component to the tree cap so it is important to prevent damage to the seals during the installation process. One way to prevent potential damage to the seals is to land the tree cap on the tree spool, secure the tree cap in the tree spool, and then energize or set the seals between the secured tree cap and the tree spool. This series of steps may lengthen and complicate the installation process. Thus, it may be beneficial to hold the seals in a non-energized state and then simultaneously secure the tree cap to the tree spool and energize the sealing elements.
The installation of a tree cap on a subsea tree spool can be difficult. Thus, it may be beneficial to provide a tree cap that does not require a particular radial orientation to land in and secure to a tree spool. The tree cap may be selectively connected to a running tool and run to the tree spool through a marine riser. In different applications, a remotely operated vehicle (“ROV”) may be used to run the tree cap to the tree spool and to remotely install the tree cap and set or energize the sealing elements. It may be beneficial to provide a tree cap that could be installed attached to a running tool ran through a marine riser or at open sea with an ROV.
An installed tree cap may project above the tree spool presenting a potential obstruction to other wellhead equipment. It may be beneficial to provide an internal tree cap having a low profile when secured to a tree spool. An installed tree cap on a tree spool creates a fluid barrier, which is beneficial to prevent the flow of fluid up the wellbore due to increases in well pressure. Increased well pressure may cause the undesired upward movement of well equipment, such as a tubing hanger, already installed in the tree spool. It would be beneficial to provide a tree cap that provides a collateral beneficial locking means for preventing undesired upward movement of well equipment due to pressure. Various configurations of tubing hangers may be employed within a tree spool. Thus, it may be beneficial to provide a tree cap that is modular enabling it to be connected to variously configured adapters to lock down differing tubing hangers.
Fluid may become trapped within the cavity of the tree cap while the tree cap is being installed onto a tree spool. This may be problematic for a light weight tree cap as the fluid may prevent the tree cap from properly landing on the tree spool. Further, the sea water may cause corrosion of some of the internal parts of the tree cap and subsea tree system such as the VX gasket. It would be beneficial to provide means for releasing trapped fluid from within the cavity of the tree cap. Further, it would be beneficial if this means also allowed for the injection of a corrosion inhibitor within the tree cap. Also a change in pressure within the wellbore may make it difficult to remove the tree cap from the tree spool. It would be beneficial to provide a flow path or other means that may be used to equalize the pressure above and below the tree cap to facilitate the removal of the tree cap from the tree spool.
A gas lift may be applied to a well in an effort to increase hydrocarbon production. Conventional tree caps may not be equipped to withstand fluid pressure within the annulus and the production bore. Thus, it may be beneficial to provide a tree cap that is equipped with bi-directional metal-to-metal seals to prevent undesired leakage of fluid through and/or around the tree cap.
In light of the foregoing, it would be desirable to provide a tree cap that may simultaneously be secured to a tree spool and energize or set a sealing element. It would also be beneficial to provide a tree cap that may be installed with a running tool through a marine riser or be installed remotely using an ROV. It would be beneficial to provide a tree cap that may be a collateral beneficial locking means for preventing upward movement of wellhead equipment, such as a tubing hanger, within a tree spool. It would be beneficial to provide the collateral beneficial locking means as a modular attachment permitting the later addition of the locking means to a tree cap. It would be beneficial to provide a tree cap that is flush with the top of the tree spool when landed and installed in the tree spool. It would be beneficial to provide a tree cap that permits the removal of water trapped between the tree cap and the subsea tree, permits the injection of fluid below the tree cap, and permits the equalization of pressure prior to the removal of the tree cap. It would also be beneficial to provide a tree cap that may be adapted to provide a seal within the tubing hanger.
The present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.